Handwritten notes made by a student days before he died have been released by his mother for the first time.
Jeremiah Duggan, 22, died in Germany in 2003 after attending a five-day conference run by the controversial Schiller Institute.
Authorities ruled he committed suicide by throwing himself in front of a car on a motorway.
But his mother Erica Duggan believes he died in a state of terror because he had never suffered depression and had phoned her the night before saying he was in trouble.
This week for the first time, Mrs Duggan revealed the notes Jeremiah took from the lectures in Wiesbaden.
Throughout, Jeremiah writes statements made about the Tavistock Institute in Hampstead.
"Modern psychology is a lie," he writes. "Psychologists are involved in manipulating - Tavistock."
Lyndon LaRouche, head of the LaRouche organisation connected to the Schiller Institute, has said the Tavistock Group is a brainwashing clinic.
Jeremiah attended counselling there when he was seven to get through his parents' divorce. This is believed to have caused disagreement between the 22-year-old and others at the conference.
Mrs Duggan said: "We went to family counselling there to come through it together.
"When we visited the Schiller Institute (after Jeremiah died), the first thing they asked us was about Jerry having been in the Tavistock.
"They were fascinated by it and we just dismissed it at the time.
"I am almost alone not only in finding out how my son died but also finding out why this organisation which preaches such things is allowed to continue.
"People just dismiss these theories as a joke but it is dangerous because people believe it."
This week, former members of the LaRouche organisation set up a website slamming the group.
The website www.laroucheplanet.info promises an "insider view on that bizarro planet of Lyndon LaRouche," from the people who "spent decades of their lives working with and for him" and "helped to build his destructive cult". It includes testimonies from former members claiming they were brainwashed.
Of the organisation, it says: "It is totalitarian by nature. The closest representation of its way of thinking is as described in George Orwell's Nineteen Eighty-Four novel."
Mrs Duggan added: "Since Jeremiah's death, former members have decided to speak out more which I think is a positive thing.
"Previously there was no information on the group - I certainly don't think Jeremiah could get any on it, now there are websites like this."
It is understood Jeremiah went to the conference believing it was just an anti-war rally and was unaware of the institute's extremist conspiracy theories and ideas surrounding Aids, the holocaust and the British monarchy.
A spokesman for the Tavistock Institute said: "There is no truth whatsoever in what he is saying we are a charitable, research consultancy and development organisation."
- LaRouche said The Beatles had no genuine musical talent – but were a product shaped according to the British Psychological Warfare Division.
- In the USA in 1988, LaRouche ran a campaign for mass Aids testing which also aimed to have sufferers quarantined.
- On the morning of the 9/11 attack, he claimed that it was an "inside job" orchestrated by Dick Cheney.
- His website www.wylm.com features campaign magazines from the 70s with articles written by other members claiming only 1.5million rather than six million Jews died in the Holocaust.
In response to this article, a spokeswoman from the Schiller Institute would only release the following statement: "The Schiller Institute has always maintained that it had no involvement in Jeremiah's death and it believes that German authorities have fully and comprehensively investigated the incident."